U.S. patent application number 14/799776 was filed with the patent office on 2017-03-16 for methods and arrangements in a telecommunication system.
The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Richard Abrahamsson, Lisa Bostrom, George Jongren, Magnus Stattin.
Application Number | 20170078073 14/799776 |
Document ID | / |
Family ID | 44913379 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170078073 |
Kind Code |
A1 |
Abrahamsson; Richard ; et
al. |
March 16, 2017 |
Methods and Arrangements in a Telecommunication System
Abstract
The present invention relates to a method and arrangement for
controlling re-transmission in a user equipment supporting uplink
spatial multiplexing. The method comprises the steps of detecting
an uplink grant on a physical downlink control channel, the uplink
grant being valid for at least one transport block; detecting that
at least one transport block is disabled, such that no grant is
associated with the at least one transport block; and interpreting
the at least one disabled transport block as an acknowledgement,
ACK, of previous transmission corresponding to said disabled
transport block irrespective of which indication is received on the
reception status feedback channel for said previous
transmission.
Inventors: |
Abrahamsson; Richard;
(Knivsta, SE) ; Bostrom; Lisa; (Solna, SE)
; Jongren; George; (Sundbyberg, SE) ; Stattin;
Magnus; (Sollentuna, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Family ID: |
44913379 |
Appl. No.: |
14/799776 |
Filed: |
July 15, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13318141 |
Oct 29, 2011 |
9136986 |
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PCT/SE2011/050929 |
Jul 8, 2011 |
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14799776 |
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61389437 |
Oct 4, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0055 20130101;
H04W 72/0453 20130101; H04L 5/0053 20130101; H04L 2001/125
20130101; H04L 1/1864 20130101; H04L 1/1896 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 72/04 20060101 H04W072/04; H04L 1/18 20060101
H04L001/18 |
Claims
1. A method for controlling re-transmission in a user equipment
supporting uplink spatial multiplexing, the method comprising the
steps of detecting an uplink grant on a physical downlink control
channel, the uplink grant being valid for at least one transport
block; detecting that at least one transport block is disabled,
such that no grant is associated with the at least one transport
block; the method being characterized b y the step of interpreting
the at least one disabled transport block as an acknowledgement,
ACK, of previous transmission corresponding to said disabled
transport block irrespective of which indication is received on the
reception status feedback channel for said previous
transmission.
2. The method according to claim 1, wherein said detecting steps
are carried out at a first protocol layer, whereby said
interpreting step comprises that the first protocol layer delivers
an indication of acknowledgement, ACK, to a second protocol
layer.
3. The method according to claim 2, wherein said indication
comprises the step of setting an ACK/NACK flag to ACK.
4. The method according to claim 1, said interpreting step
comprises that a second protocol layer assumes, upon reception from
a first protocol layer of one or more grants valid for fewer
transport blocks than what could be spatially multiplexed, that an
acknowledgement, ACK, has been received for a previous transmission
for a transport block for which no grant have been forwarded to the
second layer from the first layer.
5. The method according to claim 2, wherein the first protocol
layer is a physical layer and the second protocol layer is a higher
protocol layer.
6. The method according to claim 1, wherein said acknowledgement is
used as input in a HARQ process corresponding to said disabled
transport block in an uplink data transfer procedure.
7. An arrangement in a user equipment supporting uplink spatial
multiplexing for controlling re-transmission, the arrangement
includes a processing unit comprising circuitry configured to:
detect an uplink grant on a physical downlink control channel, the
grant being valid for at least one transport block; detect that at
least one transport block is disabled, such that no grant is
associated with the at least one transport block; characterized in
that the processing circuitry is configured to interpret the at
least one disabled transport block as an acknowledgement, ACK, of
previous transmission corresponding to said disabled transport
block irrespective of which indication is received on the reception
status feedback channel for said previous transmission.
8. The arrangement according to claim 7, wherein said processing
unit comprises processing circuitry configured to deliver an
indication of acknowledgement, ACK, from a first protocol layer to
a second protocol layer.
9. The arrangement according to claim 8, wherein said processing
unit comprises processing circuitry configured to set an ACK/NACK
flag to ACK.
10. The arrangement according to claim 7, said processing unit
comprises processing circuitry configured to assume, at a second
protocol layer, that an acknowledgement, ACK, has been received for
a previous transmission corresponding to a transport block for
which no grant have been forwarded to the higher layer from a first
protocol layer, upon reception of one or more grants valid for
fewer transport blocks than what could be spatially multiplexed
from the first protocol layer.
11. The arrangement according to claim 7, wherein the first
protocol layer is a physical layer and the second protocol layer is
a higher protocol layer.
12. The arrangement according to claim 7, wherein said processing
unit comprises processing circuitry configured to use said
acknowledgement as input in a HARQ process corresponding to said
disabled transport block in an uplink data transfer procedure.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 13/318,141
filed Oct. 29, 2011, which is a National Stage Entry of
PCT/SE2011/050929 filed on Jul. 8, 2011, which claims the benefit
of U.S. Provisional Application No. 61/389,437, filed Oct. 4, 2010,
and the contents of all of the preceding are hereby incorporated by
reference herein.
TECHNICAL FIELD
[0002] The present invention relates to control of retransmission
in a user equipment supporting uplink spatial multiplexing.
BACKGROUND
[0003] In data communication or data storage it is common practice
to transmit or store data with redundancy in a coded manner in
order to improve reliability of being able to recreate the original
message. The process is usually referred to as channel coding and
the recovery process as channel decoding. We will refer to such a
message as a code word even though in the following it does not
strictly have to be encoded.
[0004] In communication systems, such as, e.g., the Long Term
Evolution (LTE) system standardized by the Third Generation
Partnership Project (3GPP), it is also common to combine several
transmissions relating to the same code word in different
transmission time intervals (TTIs) if needed to adaptively increase
the level of redundancy to the transmission conditions. This can
for instance be done by repeating a shorter coded or uncoded
message one or several times. An alternative is to transmit a part
of a code word containing sufficient information for correct
decoding under favorable conditions, in a first transmission
attempt. If not received and decoded correctly, additional parts of
the code word can be transmitted in subsequent attempts after which
the received parts of the code word can be recombined on the
receiver side, creating a redundancy which is incremental for each
retransmission. This can then help in making sure that sufficient
but not more resources than necessary are used for transmission of
each message. For brevity we will refer to subsequent transmissions
of the same code words as retransmissions even though it may not be
the whole code word that is being retransmitted. The information
bits carried by a code word will be referred to as a transport
block (TB).
[0005] In order for transmission of subsequent code words not to be
delayed while waiting for previous messages being decoded and
potentially being (partly) retransmitted, a set of buffers
containing the data of different code words exist in parallel. This
way other buffers can be read for (re)transmission while waiting
for the previous transmission of the same transport block to be
decoded and for messages of correct/incorrect reception to be
received at the transmitter side (acknowledged (ACK) or not
acknowledged (NACK) messages). These buffers are usually referred
to as Hybrid Automatic Repeat reQuest (Hybrid ARQ or HARQ) buffers
and the process controlling each of them is referred to as a HARQ
process.
[0006] HARQ re-transmissions are handled by the Medium Access
Control (MAC) layer which is part of Layer 2 (L2) in the LTE
protocol architecture. HARQ feedback, i.e. ACK or NACK indication,
is signaled to the MAC layer from the physical layer, also referred
to as Layer 1. Layer 2 uses this information in its data transfer
process to either make a retransmission or a new transmission.
[0007] Multi-antenna techniques can significantly increase the data
rates and/or reliability of a wireless communication system. The
performance is in particular improved if both the transmitter and
the receiver are equipped with multiple antennas. This results in a
multiple-input multiple-output (MIMO) communication channel and
such systems and/or related techniques are commonly referred to as
MIMO techniques.
[0008] One MIMO technique is Spatial Multiplexing (SM), or Single
User MIMO (SU-MIMO), where one or several transport blocks relating
to one specific user are simultaneously mapped (usually linearly)
to one or several layers of data which in turn are mapped,
potentially via channel adaptive precoders (also often linear
precoders), to the different transmit antenna ports. Currently for
LTE, one or two codewords, corresponding to one or two transport
blocks, are mapped to the one or several layers of data. This way
the spatial properties of the MIMO channel can, under favorable
conditions, be exploited to transmit more data simultaneously
relating to the same user, increasing the user data throughput.
There may also be additional intermediate processing steps for
various reasons.
[0009] In LTE Release 10 (Rel. 10), the uplink (UL), which is the
communication link from user equipment to base station, or evolved
NodeB (eNB) in LTE terminology, is being extended from supporting
single-input single-output (SISO) to also support UL-Spatial
Multiplexing (UL-SM).
[0010] As in previous releases (Rel-8 and Rel-9), an UL
transmission is triggered via an uplink transmission grant
transmitted on the Physical Downlink Control Channel (PDCCH).
Retransmissions however can either be triggered by a full grant
transmitted on the PDCCH or, if no PDCCH grant is found for the
corresponding transport block, by a non-acknowledgement indication,
NACK, on the Physical HARQ Indicator Channel (PHICH) indicating
that the decoding of previous transmission attempt of the
corresponding code word failed. The former retransmission type is
usually referred to as an adaptive retransmission as the PDCCH
grant format allows for specifying a new transport format (e.g.,
modulation constellation and code rate). The latter type of
retransmission is consequently referred to as a non-adaptive
retransmission as the PHICH carries only the indication of ACK or
NACK of the previous transmission and gives no other signaling
possibility to order the UE to use a new transport format.
[0011] In LTE, UL Synchronous HARQ is employed, which means that
there is a fixed timing relation between transmission and
retransmission, hence there is a direct mapping from TTI to HARQ
process identity (ID) and this information is not needed in the UL
grant. When there are limited PDCCH resources, the base station can
therefore grant a UE an UL retransmission by a PHICH NACK alone
which then has a reduced involvement of Layer 2, L2, resources
compared to a grant received on the PDCCH. A drawback is that no
new information on transport format can then be conveyed to the UE
such as link adaptation or frequency selective rescheduling. The
reliability of the PHICH channel is also lower than that of the
PDCCH grant.
[0012] In the LTE downlink, DL, however, Asynchronous HARQ is
employed, and an explicit PDCCH assignment is needed to point out
that a DL (re)transmission is related to a specific DL HARQ
process. For DL spatial multiplexing there is therefore always an
assignment for retransmission of any code word.
[0013] This means that for LTE when DL spatial multiplexing is
configured, the physical layer, or Layer 1, L1, of the UE reads the
PDCCH for a DL assignment and when a downlink assignment is
detected, it will furthermore detect if the assignment is valid for
one or two transport blocks. This means that if the PDCCH signaling
indicates no assignment for one of the transport blocks, for
example TB1, the UE will not read the Physical Downlink Shared
Channel (PDSCH) for data for this transport block. For TB2 it will
however read the PDSCH according to the PDCCH to detect the
corresponding code word that represents data. The data is then
forwarded to L2, or the Medium Access Control (MAC) layer, and the
appropriate HARQ process for decoding.
[0014] In the case where UL-SM is configured, the UE may, for each
TTI, be assigned an UL grant that is valid for one or two TBs. It
is assumed that L1 will detect if the grant is valid for one or two
TB(s) based on the explicit PDCCH signaling, similar to how it is
done for DL spatial multiplexing. The reason for disabling a
transport block may be that the UE buffer might be empty, or the
MIMO channel may not be sufficiently rich to be able to convey
multiple data layers.
[0015] It should be noted that for spatial multiplexing the notion
of a single grant valid for one or two transport blocks is
practically equivalent to that of one or two grants valid for one
transport block each. The difference is only semantic, and is
henceforth used interchangeably.
[0016] The current 3GPP MAC Layer specification procedure for UL
data transfer is able to handle only one UL grant (or lack of UL
grant) per TTI, hence some complication can be expected when one
transport block is assigned an UL grant and the other is not. Since
these two branches are mutually exclusive in the current
specifications, it would be more straightforward to handle each
transport block separately, i.e., to assume that L2 receives
individual grants per transport block and that each transport block
is associated with a separate HARQ process. That way, the grant
reception procedure should be iterated once for each grant
associated with a certain TTI.
[0017] Assuming that the procedure is executed separately for each
transport block, the different branches could be executed for the
different cases of one transport block, e.g., TB1, having no UL
grant and the other transport block, e.g., TB2, having an UL
grant.
SUMMARY
[0018] Since Layer 1, L1, forwards only grants to Layer 2, L2, and
not absence of grants, only information of a transport block with a
valid grant will be forwarded to L2 and no information whether a
transport block without a valid grant was scheduled or disabled is
provided. L2 will then initiate its data transfer procedure for
each transport block. If a grant is received for a transport block,
an adaptive retransmission or a new transmission is performed in
accordance with the grant. Otherwise, if a non-acknowledgement
indication, NACK, is decoded for a previous transmission in the
same HARQ process for a transport block, a non-adaptive
retransmission is performed. If an acknowledgement indication, ACK,
is decoded for a previous transmission in the same HARQ process for
a transport block, no action is taken until an uplink grant is
received for said transport block. Given how re-transmissions work
in the UL, the absence of a valid UL grant for one of the transport
blocks in combination with a false decoding of a PHICH ACK, such
that the UE erroneously detects a NACK indicating a retransmission,
would cause the UE to perform a non-adaptive re-transmission, which
is not a desirable behavior. It can be assumed that the problem
occurs when any one of the two code words is disabled.
[0019] If no uplink grant is provided from the physical layer for a
HARQ process associated with a particular subframe to a higher
layer, e.g. Layer 2, the HARQ feedback on PHICH controls whether
the HARQ process should perform a non-adaptive retransmission in
that subframe. When PDCCH indicates a grant for only one HARQ
process, e.g. due to one code word corresponding to one transport
block being disabled, the control of the other HARQ process is
based on PHICH signaling which is less reliable than PDCCH
signaling. In such a case, the UE could mistakenly decode a NACK on
PHICH that was intended to be an ACK, and based on the erroneously
decoded NACK initiate a non-adaptive retransmission for that
transport block.
[0020] Thus, given the two types of re-transmissions in the UL, the
PDCCH grant triggered adaptive re-transmission and the PHICH NACK
triggered non adaptive re-transmission, it is possible that the UE,
in UL spatial multiplexing mode, is instructed to perform an
adaptive re-transmission for one TB (as ordered by PDCCH), but
since L2 does not get explicit information about the other TB being
suspended, or disabled, it would handle that TB as that it did not
get an UL grant. Executing the UL data transfer procedure for this
TB, the UE can then fail to decode an ACK on PHICH and initiate a
non-adaptive re-transmission for that TB as described above, even
though the base station may explicitly have said that it was not
needed.
[0021] The base station always has to perform the same amount of
PDCCH signaling regardless of whether it wants to schedule one or
both transport blocks, and it is assumed that there is no scenario
where it would intentionally schedule only one transport block and
want the other transport block to perform a non-adaptive
re-transmission, as an adaptive re-transmission would give better
performance. Since PDCCH has a much lower error rate than PHICH, a
solution could take advantage of this and allow the PDCCH grant
assignment to have precedence over the PHICH A/N information, even
when the PDCCH states that a specific transport block is not
assigned a grant.
[0022] Since L1 is assumed to already know if a transport block is
disabled or not from the PDCCH, the problem that the solution
presented herein identifies is that this information is not
forwarded to L2, which may result in unnecessary non-adaptive
retransmissions.
[0023] Therefore, the present invention aims to prevent the UE from
performing an accidental non-adaptive re-transmission for one or
more transport blocks.
[0024] In an aspect of the invention, a method for controlling
re-transmission in a user equipment supporting uplink spatial
multiplexing is provided. The method includes: [0025] detecting an
uplink grant on a physical downlink control channel, the uplink
grant being valid for at least one transport block; [0026]
detecting that at least one transport block is disabled, such that
no grant is associated with the at least one transport block; and
[0027] interpreting the at least one disabled transport block as an
acknowledgement, ACK, of previous transmission corresponding to
said disabled transport block irrespective of which indication is
received on the reception status feedback channel for said previous
transmission.
[0028] Said detecting steps may in a specific embodiment be carried
out at a first protocol layer, whereby said interpreting step
comprises that the first protocol layer delivers an indication of
acknowledgement, ACK, to a second protocol layer. In a specific
embodiment, said indication comprises the step of setting an
ACK/NACK flag to ACK. Said acknowledgement may be used as input in
a HARQ process corresponding to said disabled transport block in an
uplink data transfer procedure.
[0029] The first protocol layer may be a physical layer and the
second protocol layer may be a higher protocol layer.
[0030] In another aspect of the invention, an arrangement in a user
equipment supporting uplink spatial multiplexing for controlling
re-transmission is provided. The arrangement includes a processing
unit comprising circuitry configured to: [0031] detect an uplink
grant on a physical downlink control channel, the grant being valid
for at least one transport block; [0032] detect that at least one
transport block is disabled, such that no grant is associated with
the at least one transport block; and [0033] interpret the at least
one disabled transport block as an acknowledgement, ACK, of
previous transmission corresponding to said disabled transport
block irrespective of which indication is received on the reception
status feedback channel for said previous transmission.
[0034] Thus, in a particular embodiment, when L1 detects that a TB
is disabled (based on PDCCH signaling or some other method), it can
set the A/N (ACK/NACK) bit to ACK irrespective of PHICH indication
for this TB.
[0035] That way when the UL Data transfer procedure is executed
when one TB has a grant for adaptive retransmission and the other
has not, the TB without a grant will not accidentally cause a
non-adaptive re-transmission.
[0036] Other objects, advantages, and novel features of the
invention will become apparent from reading this description in
conjunction with the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The foregoing and other objects, features, and advantages of
the invention will be apparent from this detailed description as
illustrated in the drawings.
[0038] FIG. 1a is a flow chart illustrating a method according to
an embodiment of the invention.
[0039] FIG. 1b is a flow chart illustrating a method according to
another embodiment of the invention.
[0040] FIG. 2a-2b shows different scenarios for uplink spatial
multiplexing.
[0041] FIG. 3 illustrates schematically an arrangement according to
embodiments of the invention.
[0042] FIG. 4 illustrates in an alternative way an arrangement
according to embodiments of the invention.
DETAILED DESCRIPTION
[0043] In the following description, for purposes of explanation
and not limitation, specific details are set forth such as
particular architectures, interfaces, techniques, etc. in order to
provide a thorough understanding of the invention. However, it will
be apparent to those skilled in the art that the invention may be
practiced in other embodiments that depart from these specific
details. In other instances, detailed descriptions of well-known
devices, circuits, and methods are omitted so as not to obscure the
description of the invention with unnecessary details.
[0044] It should be noted that although terminology from 3GPP LTE
has been used in this disclosure to exemplify the invention, this
should not be seen as limiting the scope of the invention to only
the aforementioned system. Other wireless systems, including
Wideband Code Division Multiple Access (WCDMA), WiMax, UMB and GSM,
can also benefit from embodiments of this invention.
[0045] Also note that terminology such as base station and UE
should be considered non-limiting and does in particular not imply
a certain hierarchical relation between the two; in general "base
station" could be considered as device 1 and "UE" as device 2, and
these two devices communicate with each other over a radio channel.
Moreover, in the following description of embodiments of the
invention, the physical protocol layer will be referred to as Layer
1 and a higher protocol layer will be referred to as Layer 2. This
invention is however not limited to either Layer 1 or Layer 2.
[0046] In the following, embodiments of the invention are discussed
in order to describe in detail suitable applications of the
invention.
[0047] An illustration of a method in accordance with a particular
embodiment can be found in FIG. 1a. Upon reception of a downlink
subframe by a UE in UL-SM mode configured with N transport blocks,
such that N codewords can be spatially multiplexed, the PDCCH is
read, see step 101, and a PDCCH message that indicates at least one
UL grant for at least one transport block for a specific TTI is
detected in step 102. If one grant for each configured transport
block is detected for this TTI, see step 103, then the N grants are
forwarded in step 104 for each transport block to Layer 2, where
the procedure for Layer 2 UL data transfer for each transport block
is iterated, or initiated, 105, thereby leading to adaptive
retransmission or new code word transmission according to the
associated grants. In a particular embodiment, N=2. However, N may
also be a number larger than two.
[0048] If it is detected in step 103 that only K grants for N
transport blocks are detected for the specific TTI, where
0<K<N, see step 103, for example that only one grant
associated with a single transport block is detected for the
specific TTI, say for example TB1 and not TB2 (TB1 and TB2 can of
course be interchanged), then the disabled transport block, i.e. a
transport block for which no grant is detected, should be
interpreted such that an acknowledgement, ACK, is received for the
previous transmission corresponding to the disabled transport
block. According to this particular embodiment this is done such
that Layer 1 sets the associated ACK/NACK flag for the previous
transmission to ACK, 106, irrespective of the PHICH indication for
said previous transmission and forward the available grant(s), e.g.
for TB1, to Layer 2, see step 107 which will iterate, or initiate,
the Layer 2 data transfer procedure for each transport block, see
step 105. For a transport block with a valid grant, e.g. TB1, this
will lead to an adaptive retransmission or a new code word
transmission according to the associated grant. For any transport
block that does not have a grant, e.g. TB2, no non-adaptive
retransmission will occur since the A/N flag is set to ACK.
[0049] If on reception of the downlink subframe no grant indicating
an adaptive retransmission or new transmission is detected, and if
the PHICH is not decoded with ACK for previous transmission of
corresponding transport block or blocks any of the code words, then
Layer 1 set ACK/NACK flag to NACK for corresponding transport block
or blocks and forward this to L2, see step 108, which initiates
non-adaptive retransmission unless a desired or predetermined
maximum number of transmissions have already been done for the
corresponding code word, see step 105.
[0050] The method described above has minimal impact on the 3GPP
standard specifications. The data transfer procedure on Layer 2 is
unchanged, only initiated, or iterated, for each grant. Absence of
both grants still means that ACK/NACKS are read to determine if
non-adaptive retransmission should be made.
[0051] The above-described exemplary method uses the convention of
a separate grant for each transport block and separate HARQ
processes for each transport block, but an alternative method can
use the convention of a single grant addressing one or two
transport blocks and one HARQ process governing two code word
buffers. The practical result of both methods would be the
same.
[0052] Another embodiment is illustrated in FIG. 1b, wherein
instead of Layer 1 setting an ACK for a transport block without a
valid grant to be delivered to a higher layer, said higher layer,
e.g. Layer 2, assumes that an acknowledgement has been received for
a transmission in previous TTI for a transport block for which no
grant have been forwarded to the higher layer by the physical
layer. This assumption may for example be made by setting the
ACK/NACK flag to ACK for any transport block without a valid grant,
see step 106b, before initiating the UL data transfer procedure.
This embodiment is illustrated in FIG. 1b, in which steps 101, 102,
105 and 108 are identical to those in FIG. 1a. In step 104b,
available grants are forwarded by Layer 1 to Layer 2. In step 106b,
Layer 2 assumes any transport block for which no grant is forwarded
from Layer 1 to be disabled. In a particular embodiment, a
mechanism in Layer 2 sets an ACK/NACK flag to ACK in step 107b
irrespective of what reception status feedback, i.e. ACK or NACK,
it receives from Layer 1. In step 105, the UL data transfer
procedure is then executed for each transport block. Still with
reference to FIG. 1b, in another embodiment, Layer 2 will after
assuming any transport block for which no grant is forwarded from
L1 to be disabled in step 106b, perform the UL data transfer
procedure only for the transport block with an associated grant,
see step 109, which means that in this embodiment, Layer 2 will not
read any ACK/NACK indication from Layer 1. For a transport block
associated with a grant, this leads to an adaptive retransmission
or a new code word transmission according to the associated grant.
For the one or more transport blocks which do not have a grant, no
retransmission is initiated from L2. In such embodiment the HARQ
processes may communicate to each other whether a grant is
received, and a HARQ process that has not received a grant may
suspend itself if any other HARQ process has received a grant for
that certain TTI. When there are no grants detected L1 executes
non-adaptive retransmissions for TBs for which NACK is detected on
PHICH, see step 108.
[0053] Applications of embodiments of the invention will also be
illustrated with reference to FIGS. 2a and 2b. FIG. 2a illustrates
prior art cases 1-3 without the invention, and FIG. 2b illustrates
cases 4 and 5 where the invention is applied. In these cases it is
assumed that two transport blocks, TB1 and TB2, can be spatially
multiplexed.
[0054] Case 1
[0055] At Time 1, the UE decodes an ACK for TB1 given that an ACK
is signaled on PHICH concerning an earlier UL transmission in TB1.
At the same time, an UL grant for a new transmission at Time 1 is
received on PDCCH. Alternatively, the UE decodes a NACK given that
a NACK was signaled, then at the same time an adaptive
retransmission at Time 2 of the failed code word is granted on
PDCCH. One of the same two alternatives happens for TB2. Transport
format adaptive transmissions (either new or re-transmissions)
depending on grants at Time 1 are then transmitted on PUSCH at Time
2. For TB1, one of the same alternatives occurs for Time 3 and Time
4 as for Time 1 and Time 2. The TB2 transmission at Time 2 however
is ACKed at Time 3 but for some reason a new transmission is not
scheduled for TB2, e.g., the UE buffer might be empty, or it is
believed that the MIMO channel is not sufficiently rich to hold
multiple layers, or due to other scheduling decisions. Hence at
Time 4 there is either a new transmission or a retransmission of
TB1 according to its PDCCH grant at Time 3, but no
transmission/retransmission of TB2.
[0056] Case 2
[0057] The same alternatives happen for Time 1 and Time 2 as for
Case 1 described above. In this case, however, none of the
transmissions of the TBs lead to successful reception and are both
NACKed at Time 3. However, there are no new grants, e.g., there may
not be sufficient PDCCH resources for ordering adaptive
retransmissions of the two code words, hence the UE interprets the
NACKs such that non-adaptive retransmissions are performed at Time
4.
[0058] Case 3
[0059] Again, the same two alternatives happen for Time 1 and Time
2 as for Case 1 described above. In this case, the transmission of
one of the TBs at Time 2 is unsuccessful. Now only one of the
transport blocks, say TB1, receives an UL grant on PDCCH at Time 3.
If this TB was successfully decoded at Time 2, a new transmission
at Time 4 is triggered by the grant or an adaptive retransmission
at Time 4 is triggered if the previous transmission of the
corresponding TB was a failure resulting in an adaptive
retransmission grant. The other TB, referred to as TB2 in the FIG.
2a, which receives a NACK but no grant however would perform a
non-adaptive retransmission. Assume now that the purpose of only
one grant for TB1 was that we wanted the other TB, TB2, to be
disabled, e.g., due to poor channel conditions, and suspend the
retransmission, e.g., until more favorable channel conditions
apply, then it is not possible to distinguish these two cases and
TB2 will undesirably be subject to a L2 initiated non-adaptive
retransmission. It should also be noted that information in the
grant for TB1, e.g., precoder rank, may then also be conflicting
with the non-adaptive transport format used for TB2
retransmission.
[0060] Case 4
[0061] Now suppose that the ACK for TB2 in Case 1 above is
misinterpreted as a NACK, a non-adaptive retransmission of the
corresponding code word will erroneously be triggered according to
the current standards.
[0062] Case 5
[0063] The solution to the error Case 3 and 4 according to
embodiments of the invention is to interpret disabling of the TB as
an ACK to higher layers, which in this example means to let a grant
valid for a single TB, as in this case, always mean an ACK for the
TB without a valid grant irrespective of PHICH indication. This
means that Case 3 cannot be used to trigger a non-adaptive
retransmission at the same time as an adaptive re-transmission or
new transmission. Instead, adaptive retransmission is used together
with new transmissions or adaptive retransmission of the other TB.
The risk that an accidental non-adaptive re-transmission is
performed due to misinterpretation of the PHICH is avoided. The
overhead of using a grant also for the other TB when an explicit
grant on PDCCH is already being used for one TB is very limited or
non-existent. Moreover, the performance is better for an adaptive
retransmission than for a non-adaptive retransmission.
[0064] The two lower-most figures in case 5 illustrate how to
signal the case where one wants to retransmit one TB due to a
unsuccessful transmission while doing a new transmission or an
adaptive retransmission for the other TB, see case 3 in FIG. 2.a.
With the invention the content on PHICH and PDCCH as indicated in
case 3 will be a disabling of TB2 as a single grant on PDCCH means
ACK for TB2 irrespective of PHICH reception, hence the cross out of
the second last subfigure in FIG. 2b. To achieve retransmission of
the failed TB we explicitly grant the other TB as well, getting an
adaptive re-transmission (as the PDCCH load is the same for a
single TB grant or a two TB grant). Thus, it does not matter what
is being transmitted on PHICH as PDCCH has precedence over PHICH
(in principle no PHICH need to be transmitted, a fail to decode an
ACK will be interpreted as NACK and even a decoded ACK (erroneous
or not) will be ignored in favor of the PDCCH grant for the
adaptive retransmission.
[0065] Thus, embodiments of the invention make the communication
system more stable by preventing accidental non-adaptive
re-transmission at practically no cost in the implementation.
[0066] FIG. 3 schematically illustrates an arrangement in a user
equipment 300 in accordance with the invention that includes a
receiving unit 310 configured for reading for example PDCCH and
PHICH. The arrangement 300 furthermore includes a processing unit
320 that is configured to detect 330 a grant on a PDCCH that is
valid for at least one transport block; to detect 340 that at least
one transport block is disabled, such that no grant is associated
with the at least one transport block; and to interpret 350 the at
least one disabled transport block as reception of an
acknowledgement message ACK, irrespective of the indication on the
reception status feedback channel, e.g., the PHICH, for the
transport block. The arrangement 300 also includes a transmitting
unit 360 configured for sending information. It will be appreciated
that the processing unit 340 can be one or more suitably programmed
electronic processors or circuits and that the receiving unit 310
and transmitting unit 360 handle signals appropriate to the
particular communication system, such as LTE channels and
signals.
[0067] FIG. 4 schematically illustrates the arrangement 300 in an
alternative way. The arrangement 400 comprises an input unit 410
and an output unit 420, and a processing unit 430, which may be a
single unit or a plurality of units. The arrangement 400 further
comprises at least one computer program product 440 in the form of
a non-volatile computer-readable medium, e.g., an EEPROM, a flash
memory, and a disk drive. The computer program product includes a
computer program 450, which comprises program instructions which
when run causes the processing unit 430 to perform the steps of the
procedures described above in conjunction with FIGS. 1a-b and
3.
[0068] The program instructions, or code means, in the computer
program 450 advantageously comprises a module 450a for detecting an
uplink grant for at least one transport block, a module 450b for
detecting that at least one transport block is disabled, and a
module 450c for interpreting the at least one disabled transport
block as reception of an acknowledgement message, ACK. The program
450 can thus be implemented as computer program code structured in
computer program modules. The modules referred to above
substantially perform the steps performed by the processing unit in
FIG. 3. In other words, when the different modules are run on the
processing unit, they correspond to the configured steps
illustrated in FIGS. 1a-b and 3.
[0069] Although the program 450 in the embodiment illustrated by
FIG. 4 can be implemented as computer program modules which when
run on the processing unit cause the processing unit to perform
steps described above in the conjunction with figures mentioned
above, one or more of the code means 450 can in alternative
embodiments be implemented at least partly as hardware
circuits.
[0070] The present invention may, of course, be carried out in
other ways than those specifically set forth herein without
departing from essential characteristics of the invention. The
present embodiments are to be considered in all respects as
illustrative and not restrictive.
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